The present invention relates generally to drives for crop harvesting machinery and, more particularly, to a belt tensioning apparatus for transferring driving power from the engine to drive a combine harvester.
Belt drives transferring rotational power from a primary mover, such as an engine, to the harvesting apparatus or other drive components which are to be driven are well known. Typically, an endless belt or chain is entrained about a pair of pulleys or sprockets connected, respectively, to the power output shaft of the engine and the power input shaft of the harvester driven component. The belt will have two runs spanning the distance between the two pulleys. Depending upon the direction of power transmission, one of the runs between the drive pulley and the driven pulley will be taut and the other run will be slack.
To keep the slack side or run of the belt in proper engagement with the pulleys to enable an efficient transfer of power therebetween, a tensioning device having one or more tensioning pulleys or sprockets engageable with the slack side of the belt or chain is provided to take up the slack and properly tension the slack run of the endless member. Examples of such tensioning devices can be seen in U.S. Pat. No. 4,312,267 and in U.S. Pat. No. 3,525,269. These tensioning devices operate satisfactorily under normal operating conditions; however, under reverse power conditions, wherein the driven pulley or sprocket is driving the drive pulley or sprocket, the normally slack run becomes the taut side of the belt or chain and the normally taut run becomes slack.
Reverse power conditions can occur when the combine is going downhill. Power from the engine is cut back and gravity can cause the power input shaft to deliver more power to the belt than it is receiving from the power output shaft of the engine, whereby the direction of power transfer may be reversed with power flowing from the combine to the engine. Unless it is properly tensioned, the belt may slip on the pulleys and prevent the engine from braking the combine. Belts or chains can also become disengaged from the pulley or sprockets respectively and completely disrupt the drive transfer mechanism.
This problem is recognized relative to a drive for a motorcycle in U.S. Pat. No. 4,069,719 in which a tensioning device has a sprocket engageable with each run of an endless chain. Other drives having a tensioning idler engageable with each run of the endless flexible member can be found in U.S. Pat. Nos. 4,128,952 and 4,191,062. However, it has been found that the use of a tensioning idler to exert a tensioning force on the already taut side of a drive belt drastically reduces the life of the belt. Accordingly, it would be desirable to provide a tensioning apparatus that is operable to tension the slack side of the belt and provide minimal tensioning force on the taut side of the belt during normal operating conditions and further operable to tension the normally taut side of the belt during the aforementioned reverse power conditions while providing minimal tensioning forces to the normally slack side.